The present disclosure relates generally to immersion photolithography and, more particularly, to an apparatus and method for shielding an edge of a wafer during an immersion photolithography process.
Immersion lithography is a relatively new advancement in photolithography, in which the exposure procedure is performed with a fluid filling the space between the surface of the wafer and the lens. Using immersion lithography, higher numerical apertures can be built than when using lenses in air, resulting in improved resolution. Further, immersion lithography provides enhanced depth-of-focus (DOF) for printing ever smaller features. A photoresist or resist layer is formed on the surface of the wafer for patterning. The resist layer is applied to the surface of the wafer by a spin coating process. However, there may be resist that forms on an edge of the wafer during spin coating and, when dry, can flake off and cause particles to contaminate active areas of the wafer and/or processing equipment such as the immersion lithography system. The process wafer can also easily accumulate particles at the wafer edge area, when a solvent removes the edge resist, such particles are uncovered and may contaminate the immersion lithography system. This can lead to pattern defects, pattern distortion, and/or pattern loss.
Therefore, what is needed is a simple and cost-effective apparatus and method for shielding the edge of the wafer to minimize contaminations being introduced to the immersion lithography system.